添加对不存在二级品类的数据进行验证的逻辑

Code Review By Rock Zhang

@@ -126,6 +126,10 @@ class ClassModel
                 foreach ($data as $item) {
                     $id = $item['category_id'];
                     $result['first'][$id] = $item['category_name'];
+                    if (!isset($item['sub'])) {
+                        continue;
+                    }
+
                     foreach ($item['sub'] as $sub) {
                         $id = $sub['category_id'];
                         $result['second'][$id] = $sub['category_name'];